Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Type and Company's Internal Credit Quality Rating (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 223,351	$ 223,329
Total outstanding commitments	451,359	451,841
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	66,323	66,223
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	37,400	36,953
Residential mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	45,984	44,018
Credit card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,229	17,115
Other retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,680	47,712
Total loans, excluding covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	212,616	212,021
Covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,735	11,308
Pass Internal Credit Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	216,361	215,731
Total outstanding commitments	442,045	442,047
Pass Internal Credit Rating [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	64,167	63,906
Pass Internal Credit Rating [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	34,832	34,096
Pass Internal Credit Rating [Member] | Residential mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	44,887	42,897
Pass Internal Credit Rating [Member] | Credit card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,898	16,752
Pass Internal Credit Rating [Member] | Other retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,257	47,294
Pass Internal Credit Rating [Member] | Total loans, excluding covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	206,041	204,945
Pass Internal Credit Rating [Member] | Covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,320	10,786
Special Mention Criticized Internal Credit Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,739	1,850
Total outstanding commitments	3,181	3,231
Special Mention Criticized Internal Credit Rating [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,005	1,114
Special Mention Criticized Internal Credit Rating [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	626	621
Special Mention Criticized Internal Credit Rating [Member] | Residential mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12	18
Special Mention Criticized Internal Credit Rating [Member] | Other retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	35	36
Special Mention Criticized Internal Credit Rating [Member] | Total loans, excluding covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,678	1,789
Special Mention Criticized Internal Credit Rating [Member] | Covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	61	61
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,251	5,748
Total outstanding commitments	6,133	6,563
Classified Criticized [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,151	1,203
Classified Criticized [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,942	2,236
Classified Criticized [Member] | Residential mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,085	1,103
Classified Criticized [Member] | Credit card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	331	363
Classified Criticized [Member] | Other retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	388	382
Classified Criticized [Member] | Total loans, excluding covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,897	5,287
Classified Criticized [Member] | Covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	354	461
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,990	7,598
Total outstanding commitments	9,314	9,794
Total Criticized [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,156	2,317
Total Criticized [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,568	2,857
Total Criticized [Member] | Residential mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,097	1,121
Total Criticized [Member] | Credit card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	331	363
Total Criticized [Member] | Other retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	423	418
Total Criticized [Member] | Total loans, excluding covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,575	7,076
Total Criticized [Member] | Covered loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 415	$ 522